In an open, wireless communications network such as a cellular telephone network, a communication terminal seeking to join the network may not initially know which logical communication channels can be used to communicate with other communication terminals or base stations within the network. Joining the network, therefore, can require a potentially extensive channel search or scan which can consume significant time and energy resources.
To reduce the expected time and energy resources dedicated to channel scanning activities, several solutions have been proposed which attempt to leverage known information to reduce the number of scans performed by scanning deemed more likely channel candidates earlier or more frequently than deemed less likely candidates.
U.S. Pat. No. 5,517,677 discloses a channel scanning technique that is preferential to communication channels actually utilized in the past. A scanning cycle of channels or frequencies to be scanned is defined, in which preferred frequencies are scanned multiple times early in the cycle. When a scanned frequency is revealed to be functional for connecting to a desired wireless network, the cycle is redefined, so that this scanned frequency will be scanned more often in the future. Geographic location can also be used to influence the scanning cycle.
United States Patent Application Publication No. US 2007/0254649 similarly discloses an adaptive scanning method in which an initial list of channels to be scanned is updated by temporarily “marking” channels having qualified activity, such that these marked channels are scanned at a higher periodic rate for a predetermined number of scan cycles.
U.S. Pat. Nos. 6,192,223 and 6,941,120 both disclose a frequency scanning radio receiver which updates a scanning list based on geographical information, for example as collected by the communications terminal via a Global Positioning System. Geographical information is used to look up a database of frequency allocation data, which provides a list of preferred scanning frequencies.
International Patent Application Publication No. WO 00/78075 discloses a method of scanning sub-carrier frequencies in which sets of frequencies are scanned in order based on a perceived likelihood of successful use. The first set of frequencies scanned corresponds to a stored list of frequencies known to be in use without regard to operator identity or geographic location. Additional sets of frequencies may then be scanned in turn, wherein lists of frequencies with perceived higher likelihood of successful use are scanned first. A combination of predefined and updatable lists is also disclosed, wherein lists may be updated based on the history of successful network connections.
Recently, flexible communications terminals, such as multi-mode cellular telephones, have been introduced which allow for connection to different types of wireless networks with a single device. For example, dual-mode cellular handsets are available which can connect to either a GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telecommunications System) network, depending on availability. When such a flexible terminal seeks to join a network, it must not only scan for an available channel, but must also scan for an available network type. Since different communication modes can rely on substantially different technologies, scans for networks operating in each mode may require substantially different operations.
Conventional single-mode adaptive scanning solutions, such as described above, do not account for the potential multi-mode operation of flexible communications terminals. As such, a flexible communications terminal such as a multi-mode cellular handset would be required to perform multiple, independent single-mode scans in order to find a desired communication network operating on an unknown channel and in an unknown mode. This can be inefficient in terms of scan time and energy usage since information gathered during a channel scan for networks operating in one mode is not used during subsequent channel scans for networks operating in other modes.
Therefore, there is a need for a method of scanning a network that scans for networks in multiple communication modes and adapts scan behaviour based on the results of previous scans.